Pulsative venous return from the branchial vessels to the heart of the bivalve Mytilus galloprovincialis supports the constant-volume mechanism.

In bivalves and gastropods, ventricle contraction causes a negative pressure in the auricles and increases venous return from the afferent oblique vein (AOV): the constant-volume (CV) mechanism. The flow in the AOV should be a pulsative flow synchronized with the ventricular contraction. The flow in the heart and adjacent vessels of Mytilus galloprovincialis were measured by magnetic resonance imaging to confirm this hypothesis. Under a regular heartbeat, pulsative flows in the AOV and branchial vessels (BVs) were almost completely synchronized with the flow in the aorta, while filling of the ventricle was in the opposite phase. Flows in the BVs were directed to the posterior direction, and a pair of BVs in the gill axes (the efferent BVs) were connected to the AOV. Based on the images of the whole pathway of the AOV in an oblique slice, we confirmed that haemolymph flow was evoked from the efferent BVs and flow into the ventricle via the auricle was completed in a single heartbeat. Therefore, the walls of the AOV and BVs could resist negative transmural pressure caused by the ventricular contraction. In conclusion, the auricle, the AOV and the BVs, including the gill filaments, act as a suction pump. The pulsative venous return is driven by the negative pressure of the AOV as in the CV mechanism, and the negative pressure in the efferent BVs could draw haemolymph from the sinus via the gill and the afferent BVs. Therefore, Mytilus can start and stop its heartbeat as necessary.

The role of warming in modulating neodymium effects on adults and sperm of Mytilus galloprovincialis.

The use of rare earth elements (REEs) has been increasing and one of the most used is neodymium (Nd). Being an emergent contaminant, its negative impacts are poorly understood. Aquatic organisms are also threatened by climate change-related factors, as is the case of warming, which can change the effects of REEs. Thus, the impacts of Nd, warming, and the combination of both stressors were studied in adult mussels and sperm of the species Mytilus galloprovincialis, after an exposure period of 28 days (adults) and 30 min (sperm). The effects were evaluated through the analysis of biochemical and histopathological alterations in adults and biochemical and physiological responses given by sperm. The results showed that mussels only activated their biotransformation capacity when exposed to the stressors acting alone, which was insufficient to avoid lipid peroxidation. Furthermore, warming (alone and combined with Nd) also produces damage to proteins. The digestive gland was the most sensitive organ to Nd, presenting several histopathological alterations. In the case of sperm, all stressors induced lipid peroxidation, a higher oxygen demand, and a decrease in velocity, even if the sperm viability was maintained. It seems that warming influenced the effects of Nd to some extent. The present findings contribute significantly to the field of REEs environmental toxicology by offering valuable insights into the impacts of Nd on various biological levels of mussels. Additionally, within the context of climate change, this study sheds light on how temperature influences the effects of Nd. The obtained results indicate that both stressors can potentially compromise the overall health of mussel populations, thereby affecting other species reliant on them for food and habitat. Moreover, this study highlights impaired sperm health, which could adversely affect their reproductive capacity and ultimately lead to population decline.

Mytilus galloprovincialis releases immunologically functional haemocytes to the intervalvar space in response to tissue injury and infection.

Haemocytes of Mytilus galloprovincialis represent the main component of the internal self-defence system. Although haemocytes from haemolymph are usually studied to analyse these animals' immune response, the presence of haemocytes in the intervalvar liquid, which is essentially sea water, led us to characterize them. Several functional (ROS production, phagocytosis, gene expression, travel velocity and distance) and morphological (area, size and granularity) assays were performed by applying different stimuli to the mussels (waterborne infection, shell injury and their combination). Our results revealed that intervalvar liquid haemocytes share common characteristics with haemolymph haemocytes (for instance, the cell morphology and the cell population structure divided in three main groups) but also show significant differences in size (usually smaller in the intervalvar liquid), mobility (commonly faster in the intervalvar liquid), ROS production (higher in non-stimulated intervalvar liquid cells) and gene expression (IL17, Myd88 and CathL are over expressed in liquid intervalvar cells compared to haemolymph cells). Moreover, differences were observed when mussels were subjected to the mentioned treatments. These free intervalvar haemocytes could constitute the first line of defence as external sentinels extending the immunological alert system outside of the mussel body.

Outer membrane vesicles induce the mussel plantigrade settlement via regulation of c-di-GMP.

Despite the importance of outer membrane vesicles (OMVs) in benthic animal settlement, the underlying molecular mechanism remains elusive. Here, the impact of OMVs and OMVs synthesis-related tolB gene in Mytilus coruscus plantigrade settlement was tested. The OMVs were extracted from Pseudoalteromonas marina through density gradient centrifugation, and a tolB knockout strain, achieved by homologous recombination, was utilized for the investigation. Our results demonstrated that OMVs could significantly enhance M. coruscus plantigrades settlement. Deleting the tolB resulted in downregulation of c-di-GMP, accompanied by a reduction of OMV production, a decline in bacterial motility and increasing biofilm-forming ability. Enzyme treatment resulted in a 61.11% reduction in OMV-inducing activity and a 94.87% reduction in LPS content. Thus, OMVs regulate mussel settlement via LPS, and c-di-GMP is responsible for the OMV-inducing capacity. These findings provide new insights into the interactions between bacteria and mussels.

Modeling integrated biomarker response (IBR) index for the mussel Mytilus galloprovincialis (Lamark 1819) exposed to heavy metal mixture using the CCF design.

Marine pollutants such as heavy metals (HMs) are considered among the most copious oxidative stress (OS) inducers in marine organisms which leads to reactive oxygen species (ROS) formation. Complementary to our previous bioassays studies, the present research focuses on Catalase (CAT), Glutathione S-transferase (GST) and Malondialdehyde (MDA) as oxidative stress biomarkers and the integrated biomarker response (IBR) indexes (IBR1 and IBR2) as an ecotoxicological assessment tool in Mytilus galloprovincialis using central composite face centered (CCF) design. The oxidative stress biomarkers were measured in adult mussels (45-55 mm) on 3 days-exposed under different sub-lethal concentrations of cadmium (Cd), zinc (Zn), and copper (Cu). Using multiple regressions, ANOVA analysis revealed that experimental data fitted to second-order (quadratic) polynomial equations. The results showed that types, concentrations and metals combinations has a direct effect in CAT and GST activities, MDA level and IBR indexes. Additionally, metal-metal interactions were found synergistic (supra-additive), antagonistic (infra-additive) or zero interaction in the toxicological effect. As necessary, the optimization of the experimental results was done in order to determine the optimal conditions for the oxidative stress responses and IBR indexes. It was demonstrated that the CCF design combined with the multi-biomarker approach and IBR index can be used as an appropriate tool in ecotoxicological modulation and prediction of oxidative stress and antioxidant status by heavy metals in the mussels Mytilus galloprovincialis.

Symbiont-induced phenotypic variation in an ecosystem engineer mediates thermal stress for the associated community.

Microbial symbionts have strong potential to mediate responses to climate change. Such modulation may be particularly important in the case of hosts that modify the physical habitat structure. By transforming the habitats, ecosystem engineers alter resource availability and modulate environmental conditions which, in turn, indirectly shape the community associated with that habitat. Endolithic cyanobacteria are known to reduce the body temperatures of infested mussels and here, we assessed whether the thermal benefits of endoliths on the intertidal reef-building mussel Mytilus galloprovincialis extends to the invertebrate community utilising mussel beds as habitat. Artificial reefs of biomimetic mussels either colonised or not colonised by microbial endoliths were used to test whether infauna species (the limpet Patella vulgata, the snail Littorina littorea and mussel recruits) in a mussel bed with symbionts experience lower body temperatures than those within a bed composed of mussels without symbionts. We found that infaunal individuals benefitted from being surrounded by mussels with symbionts, an effect that may be particularly critical during intense heat stress. Indirect effects of biotic interactions, complicate our understanding of community and ecosystem responses to climate change, especially in cases involving ecosystem engineers, and accounting for them will improve our predictions.

Effects of heat acclimation on cardiac function in the intertidal mussel Mytilus californianus: can laboratory-based indices predict survival in the field?

Thermal performance curves are commonly used to investigate the effects of heat acclimation on thermal tolerance and physiological performance. However, recent work indicates that the metrics of these curves heavily depend on experimental design and may be poor predictors of animal survival during heat events in the field. In intertidal mussels, cardiac thermal performance (CTP) tests have been widely used as indicators of animals' acclimation or acclimatization state, providing two indices of thermal responses: critical temperature (Tcrit; the temperature above which heart rate abruptly declines) and flatline temperature (Tflat; the temperature where heart rate ceases). Despite the wide use of CTP tests, it remains largely unknown how Tcrit and Tflat change within a single individual after heat acclimation, and whether changes in these indices can predict altered survival in the field. Here, we addressed these issues by evaluating changes in CTP indices in the same individuals before and after heat acclimation. For control mussels, merely reaching Tcrit was not lethal, whereas remaining at Tcrit for ≥10 min was lethal. Heat acclimation significantly increased Tcrit only in mussels with an initially low Tcrit (<35°C), but improved their survival time above Tcrit by 20 min on average. Tflat increased by ∼1.6°C with heat acclimation, but it is unlikely that increased Tflat improves survival in the field. In summary, Tcrit and Tflat per se may fall short of providing quantitative indices of thermal tolerance in mussels; instead, a combination of Tcrit and tolerance time at temperatures ≥Tcrit better defines changes in thermal tolerance with heat acclimation.

Bivalves maintain repair when faced with chronically repeated mechanical stress.

Even though mollusks' capacity to repair shell damage is usually studied in response to a single event, their shells have to defend them against predatory and environmental threats throughout their potentially multi-decadal life. We measured whether and how mollusks respond to chronic mechanical stress. Once a week for 7 months, we compressed whole live California mussels (Mytilus californianus) for 15 cycles at ∼55% of their predicted one-time breaking force, a treatment known to cause fatigue damage in shells. We found mussels repaired their shells. Shells of experimentally stressed mussels were just as strong at the end of the experiment as those of control mussels that had not been experimentally loaded, and they were more heavily patched internally. Additionally, stressed shells differed in morphology; they were heavier and thicker at the end of the experiment than control shells but they had increased less in width, resulting in a flatter, less domed shape. Finally, the chronic mechanical stress and repair came at a cost, with stressed mussels having higher mortality and less soft tissue than the control group. Although associated with significant cost, mussels' ability to maintain repair in response to ongoing mechanical stress may be vital to their survival in harsh and predator-filled environments.

The influence of stochastic temperature fluctuations in shaping the physiological performance of the California mussel, Mytilus californianus.

Climate change is forecasted to increase temperature variability and stochasticity. Most of our understanding of thermal physiology of intertidal organisms has come from laboratory experiments that acclimate organisms to submerged conditions and steady-state increases in temperatures. For organisms experiencing the ebb and flow of tides with unpredictable low tide aerial temperatures, the reliability of reported tolerances and thus predicted responses to climate change requires incorporation of environmental complexity into empirical studies. Using the mussel Mytilus californianus, our study examined how stochasticity of the thermal regime influences physiological performance. Mussels were acclimated to either submerged conditions or a tidal cycle that included either predictable, unpredictable or no thermal stress during daytime low tide. Physiological performance was measured through anaerobic metabolism, energy stores and cellular stress mechanisms just before low tide, and cardiac responses during a thermal ramp. Both air exposure and stochasticity of temperature change were important in determining thermal performance. Glycogen content was highest in the mussels from the unpredictable treatment, but there was no difference in the expression of heat shock proteins between thermal treatments, suggesting that mussels prioritise energy reserves to deal with unpredictable low tide conditions. Mussels exposed to fluctuating thermal regimes had lower gill anaerobic metabolism, which could reflect increased metabolic capacity. Our results suggest that although thermal magnitude plays an important role in shaping physiological performance, other key elements of the intertidal environment complexity such as stochasticity, thermal variability and thermal history are also important considerations for determining how species will respond to climate warming.

Metabolic remodeling caused by heat hardening in the Mediterranean mussel Mytilus galloprovincialis.

Organisms can modify and increase their thermal tolerance faster and more efficiently after a brief exposure to sublethal thermal stress. This response is called 'heat hardening' as it leads to the generation of phenotypes with increased heat tolerance. The aim of this study was to investigate the impact of heat hardening on the metabolomic profile of Mytilus galloprovincialis in order to identify the associated adjustments of biochemical pathways that might benefit the mussels' thermal tolerance. Thus, mussels were exposed sequentially to two different phases (heat hardening and acclimation phases). To gain further insight into the possible mechanisms underlying the metabolic response of the heat-hardened M. galloprovincialis, metabolomics analysis was complemented by the estimation of mRNA expression of phosphoenolpyruvate carboxykinase (PEPCK), pyruvate kinase (PK) and alternative oxidase (AOX) implicated in the metabolic pathways of gluconeogenesis, glycolysis and redox homeostasis, respectively. Heat-hardened mussels showed evidence of higher activity of the tricarboxylic acid (TCA) cycle and diversification of upregulated metabolic pathways, possibly as a mechanism to increase ATP production and extend survival under heat stress. Moreover, formate and taurine accumulation provide an antioxidant and cytoprotective role in mussels during hypoxia and thermal stress. Overall, the metabolic responses in non-heat-hardened and heat-hardened mussels underline the upper thermal limits of M. galloprovincialis, set at 26°C, and are in accordance with the OCLTT concept. The ability of heat-hardened mussels to undergo a rapid gain and slow loss of heat tolerance may be an advantageous strategy for coping with intermittent and often extreme temperatures.

Ocean acidification alters sperm responses to egg-derived chemicals in a broadcast spawning mussel.

The continued emissions of anthropogenic carbon dioxide are causing progressive ocean acidification (OA). While deleterious effects of OA on biological systems are well documented in the growth of calcifying organisms, lesser studied impacts of OA include potential effects on gamete interactions that determine fertilization, which are likely to influence the many marine species that spawn gametes externally. Here, we explore the effects of OA on the signalling mechanisms that enable sperm to track egg-derived chemicals (sperm chemotaxis). We focus on the mussel Mytilus galloprovincialis, where sperm chemotaxis enables eggs to bias fertilization in favour of genetically compatible males. Using an experimental design based on the North Carolina II factorial breeding design, we test whether the experimental manipulation of seawater pH (comparing ambient conditions to predicted end-of-century scenarios) alters patterns of differential sperm chemotaxis. While we find no evidence that male-female gametic compatibility is impacted by OA, we do find that individual males exhibit consistent variation in how their sperm perform in lowered pH levels. This finding of individual variability in the capacity of ejaculates to respond to chemoattractants under acidified conditions suggests that climate change will exert considerable pressure on male genotypes that can withstand an increasingly hostile fertilization environment.

Density-Dependent and Species-Specific Effects on Self-Organization Modulate the Resistance of Mussel Bed Ecosystems to Hydrodynamic Stress.

AbstractSelf-organized, regular spatial patterns emerging from local interactions among individuals enhance the ability of ecosystems to respond to environmental disturbances. Mussels self-organize to form large, regularly patterned biogenic structures that modify the biotic and abiotic environment and provide numerous ecosystem functions and services. We used two mussel species that form monospecific and mixed beds to investigate how species-specific behavior affects self-organization and resistance to wave stress. Perna perna has strong attachment but low motility, while Mytilus galloprovincialis shows the reverse. At low density, the less motile P. perna has limited spatial self-organization compared with M. galloprovincialis, while when coexisting, the two species formed random spatial patterns. At high density, the two species self-organized in similar ways, while when coexisting, patterns were less strong. Spatial pattern formations significantly shaped resistance to hydrodynamic stress. At low density, P. perna beds with strong attachment and M. galloprovincialis beds with strong spatial organization showed higher retention rates than mixed beds. At high density, the presence of strongly attached P. perna significantly increased retention in mixed and P. perna beds compared with M. galloprovincialis beds. Our study emphasizes the importance of the interplay of species-specific behaviors to spatial self-organization and stress tolerance in natural communities.

Time-dependent metabolic disorders induced by short-term exposure to polystyrene microplastics in the Mediterranean mussel Mytilus galloprovincialis.

In the modern society, plastic has achieved a crucial status in a myriad of applications because of its favourable properties. Despite the societal benefits, plastic has become a growing global concern due to it is persistence and bioavailability as microplastics (MPs) to aquatic biota. In order to provide mechanistic insights into the early toxicity effects of MPs on aquatic invertebrates, a short-term (up to 72 h) exposure to 3 µm red polystyrene MPs (50 particles/mL) was conducted on marine mussels Mytilus galloprovincialis, selected as model organism for their ability to ingest MPs and their commercial relevance. The use of protonic Nuclear Magnetic Resonance (1H NMR)-based metabolomics, combined with chemometrics, enabled a comprehensive exploration at fixed exposure time-points (T24, T48, T72) of the impact of MPs accumulated in mussel digestive glands, chosen as the major site for pollutants storage and detoxification processes. In detail, 1H NMR metabolic fingerprints of MP-treated mussels were clearly separated from control and grouped for experimental time-points by a Principal Component Analysis (PCA). Numerous metabolites, including amino acids, osmolytes, metabolites involved in energy metabolism, and antioxidants, participating in various metabolic pathways significantly changed over time in MP-exposed mussel digestive glands related to control, reflecting also the fluctuations in MPs accumulation and pointing out the occurrence of disorders in amino acid metabolism, osmotic equilibrium, antioxidant defense system and energy metabolism. Overall, the present work provides the first insights into the early mechanisms of toxicity of polystyrene MPs in marine invertebrates.

Stress responses in expressions of microRNAs in mussel Mytilus galloprovincialis exposed to cadmium.

MicroRNAs (miRNAs) are known to have complicated functions in aquatic species, but little is known about the role of miRNAs in mollusk species under environmental stress. In this study, we performed small RNA sequencing to characterize the differentially expressed miRNAs in different tissues (whole tissues, digestive glands, gills, and gonads) of blue mussels (Mytilus galloprovincialis) exposed to cadmium (Cd). In summary, 107 known miRNAs and 32 novel miRNAs were significantly (p < 0.01) differentially expressed after Cd exposure. The peak size of miRNAs was 22 nucleotides. Target genes of these differentially expressions of miRNAs related to immune defense, apoptosis, lipid and xenobiotic metabolism showed significant changes under Cd stress. These findings provide the first characterization of miRNAs in mussel M. galloprovincialis and expressions of many target genes in response to Cd stress.

A single heat-stress bout induces rapid and prolonged heat acclimation in the California mussel, Mytilus californianus.

Climate change is not only causing steady increases in average global temperatures but also increasing the frequency with which extreme heating events occur. These extreme events may be pivotal in determining the ability of organisms to persist in their current habitats. Thus, it is important to understand how quickly an organism's heat tolerance can be gained and lost relative to the frequency with which extreme heating events occur in the field. We show that the California mussel, Mytilus californianus-a sessile intertidal species that experiences extreme temperature fluctuations and cannot behaviourally thermoregulate-can quickly (in 24-48 h) acquire improved heat tolerance after exposure to a single sublethal heat-stress bout (2 h at 30 or 35°C) and then maintain this improved tolerance for up to three weeks without further exposure to elevated temperatures. This adaptive response improved survival rates by approximately 75% under extreme heat-stress bouts (2 h at 40°C). To interpret these laboratory findings in an ecological context, we evaluated 4 years of mussel body temperatures recorded in the field. The majority (approx. 64%) of consecutive heat-stress bouts were separated by 24-48 h, but several consecutive heat bouts were separated by as much as 22 days. Thus, the ability of M. californianus to maintain improved heat tolerance for up to three weeks after a single sublethal heat-stress bout significantly improves their probability of survival, as approximately 33% of consecutive heat events are separated by 3-22 days. As a sessile animal, mussels likely evolved the capability to rapidly gain and slowly lose heat tolerance to survive the intermittent, and often unpredictable, heat events in the intertidal zone. This adaptive strategy will likely prove beneficial under the extreme heat events predicted with climate change.

Post-ejaculation thermal stress causes changes to the RNA profile of sperm in an external fertilizer.

Sperm cells experience considerable post-ejaculation environmental variation. However, little is known about whether this affects their molecular composition, probably owing to the assumption that sperm are transcriptionally quiescent. Nevertheless, recent evidence shows sperm have distinct RNA profiles that affect fertilization and embryo viability. Moreover, RNAs are expected to be highly sensitive to extracellular changes. One such group of RNAs are heat shock protein (hsp) transcripts, which function in stress responses and are enriched in sperm. Here, we exploit the experimental tractability of the mussel Mytilus galloprovincialis by exposing paired samples of ejaculated sperm to ambient (19°C) and increased (25°C) temperatures, then measure (i) sperm motility phenotypes, and (ii) messenger RNA (mRNA) levels of two target genes (hsp70 and hsp90) and several putative reference genes. We find no phenotypic changes in motility, but reduced mRNA levels for hsp90 and the putative reference gene gapdh at 25°C. This could reflect either decay of specific RNAs, or changes in translation and degradation rates of transcripts to maintain sperm function under stress. These findings represent, to our knowledge, the first evidence for changes in sperm RNA profiles owing to post-ejaculation environments, and suggest that sperm may be more vulnerable to stress from rising temperatures than currently thought.

BDE-47 exposure modulates cellular responses, oxidative stress and biotransformation related-genes in Mytilus galloprovincialis.

Polybrominated diphenyl ethers (PBDEs) are flame retardants, characterized by elevated stability in the marine environment, where are accumulated by organisms, inducing a wide panel of negative effects. In this study, some biochemical patterns related to toxicity, biotransformation and oxidative stress, were studied in the marine model system, Mytilus galloprovincialis, exposed to BDE-47. Mussels were fed with microalgae, previously treated with increasing concentrations of PBDEs (maximum dose 100 ng L-1 of BDE-47 per day). After 15 days of treatment, mussels were fed with the same diet without BDE-47, for additional 15 days. Gills and digestive glands were analyzed at T 0, at 15 and 30 days. Histopathological lesions were assessed in digestive glands of contaminated mussels, while expression of genes, related to cell cycle, multidrug resistance, oxidative stress and detoxification was evaluated on both gills and digestive glands. After 15 days, BDE-47 exposure significantly affected the cell activity in digestive gland and, at 30 days, only mussels exposed to the lower doses showed a certain recovery. Regarding the gene expression, both gills and digestive glands showed a significant down-regulation of the target genes at 15 days, although most of them were up-regulated at 30 days in digestive gland. The results on BDE-47 accumulation in mussels revealed a dose-dependent concentration in tissues, which remained elevated after further 15 days of depuration. This trend supports the responses of the biomarkers, indicating that exposure, at environmentally realistic concentrations of BDE-47, strongly modulates oxidative stress and related patterns of gene expression, suggesting concerns for long-term effect in the biota.

Spatial Dynamics and Spread of Ecosystem Engineers: Two Patch Analysis.

Ecosystem engineers are organisms characterized by interacting with other organisms thorough physical modifications or modifying their habitat. Examples of ecosystem engineers include Spartina alterniflora cordgrass or the zebra mussel Dreissena polymorpha. For both of these, the effect of modifying the environment can be nonlocal, affecting other regions farther away from the region populated by the ecosystem engineer. This shows the importance of understanding the population dynamics of ecosystem engineers in a spatial context. To do this, we have developed an extension of the ecosystem engineer population model of Cuddington et al. (Am Natur, 2009. https://doi.org/10.1086/597216 ) to the simplest spatial model, incorporating two local populations. We use this model to understand the relationship between dispersal and engineering effects, both at local and regional scales. Our main result is that the delayed Allee effect induced in the nonspatial model is extended to the spatial model, so the spread dynamics of an ecosystem engineer can be similar to the Allee case. However, there are more complex possibilities due to the two components of the dynamics. We also find quantitative guidelines that explain the interaction between spread of the environment modification and organism spread.

Motility of the Labial Palps in Feeding Behavior and its Innervation in the Marine Mussel, Mytilus galloprovincialis.

The labial palps of bivalves are thought to be involved in suspension feeding. However, the function of their muscular movements and neural regulation are still unclear. In semi-intact preparations of Mytilus, in which one valve was removed, suspended particles were removed from the labial palps following two kinds of compound movements: torsional and rotational. Both of these compound movements are therefore thought to function in rejection during feeding. These movements were observed in reduced preparations of isolated labial palps with intact cerebral ganglia, and were maintained even after removal of the cerebral ganglia, suggesting that they are generated by the peripheral neural network. Stimulation of the anterior pallial nerve elicited tetanic contraction of the labial palp, followed by secondary responses, including torsional movement. Secondary responses were dramatically reduced by a high concentration of divalent cations, in which polysynaptic pathways were inhibited. Hence, the cerebral ganglia may play an excitatory role within the peripheral neural network and the labial palp musculature via the anterior pallial nerve. Administration of serotonin induced repetitive muscular movements, whereas dopamine did not induce muscular movements. Serotonin-induced muscular movements were not elicited under a high concentration of divalent cation condition. In histochemical experiments, both the serotonergic and dopaminergic neural processes and cell body-like structures were widely observed inside the labial palp, the anterior pallial nerve, and the cerebral ganglia. Serotonin may thus contribute to activation of polysynaptic peripheral pathways, which are involved in regulating compound movements.

Characterization of a novel shell matrix protein with vWA domain from Mytilus coruscus.

Mollusk shell is a product of biomineralization with excellent mechanical properties, and the shell matrix proteins (SMPs) have important functions in shell formation. A vWA domain-containing protein (VDCP) was identified from the shell of Mytilus coruscus as a novel shell matrix protein. The VDCP gene is expressed at a high level in specific locations in the mantle and adductor muscle. Recombinant VDCP (rVDCP) showed abilities to alter the morphology of both calcite and aragonite, induce the polymorph change of calcite, bind calcite, and decrease the crystallization rate of calcite. In addition, immunohistochemistry analyses revealed the specific location of VDCP in the mantle, the adductor muscle, and the myostracum layer of the shell. Furthermore, a pull-down analysis revealed eight protein interaction partners of VDCP in shell matrices and provided a possible protein-protein interaction network of VDCP in the shell.